Citable URI

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Abstract

A polyclonal antibody (C4), raised against the head domain of chicken myosin Va,
reacted strongly towards a 65 kDa polypeptide (p65) on western blots of extracts from squid optic
lobes but did not recognize the heavy chain of squid myosin V. This peptide was not recognized by
other myosin Va antibodies, nor by an antibody specific for squid myosin V. In an attempt to
identify it, p65 was purified from optic lobes of Loligo plei by cationic exchange and reverse phase
chromatography. Several peptide sequences were obtained by mass spectroscopy from p65 cut from
SDS-PAGE gels. BLAST analysis and partial matching with ESTs from a Loligo pealei data bank
indicated that p65 contains consensus signatures for the hnRNP A/B family of RNA-binding
proteins. Centrifugation of post mitochondrial extracts from optic lobes on sucrose gradients after
treatment with RNase gave biochemical evidence that p65 associates with cytoplasmic RNP
complexes in an RNA-dependent manner. Immunohistochemistry and immunofluorescence studies
using the C4 antibody showed partial co-labeling with an antibody against squid synaptotagmin in
bands within the outer plexiform layer of the optic lobes and at the presynaptic zone of the stellate
ganglion. Also, punctate labeling by the C4 antibody was observed within isolated optic lobe
synaptosomes. The data indicate that p65 is a novel RNA-binding protein located to the presynaptic
terminal within squid neurons and may have a role in synaptic localization of RNA and its
translation or processing.

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